JPH10263754A - Method for changing mold width in continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of scratch on the wall surface in the long sides of a mold by deccelerating the casting speed to the speed without causing inclusion defect in the case of impressing no magnetic field, stopping the impression of the magnetic field, executing the change of mold width, restarting the impression of the magnetic field after completing the change of the width, and accelerating the casting speed to the ordinary speed. SOLUTION: The mold for continuos casting is constituted with the mold long side walls 1a, 1b and the mold short side walls 2a, 2b. The impression of the magnetic field is stopped and the mold short side walls 2a, 2b are shifted. Scale, etc., stuck to the mold long side walls 1a, 1b and the mold short side walls 2a, 2b with the magnetic force is separated from the walls by stopping the impression. During moving the mold short side walls 2a, 2b, the scale is not entered into gaps 7a, 7b, 8a, 8b of the short side copper plates with the long side copper plates between the long side walls 1a, 1b and the short side walls 2a, 2b, and the scratch on the mold long side wall surfaces 9a, 9b is not caused. The casting speed at the time of stopping the magnetic field is 4/5-9/10 of the ordinary speed preferably.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of changing a mold width during casting in continuous casting, and more particularly to a method of changing a mold width during casting in a continuous casting method applying a static magnetic field.

[0002]

2. Description of the Related Art In the field of continuous casting of steel, a technique for controlling the flow of molten steel in a continuous casting mold by applying a static magnetic field to improve the internal quality of a slab strand has been developed. Especially under the application of such technology,
When moving the short side wall of the mold to change the width of the slab strand without interrupting continuous casting, abrasion occurs on the wall of the long side wall of the mold that sandwiches the short side wall of the mold, and if casting is continued as it is, This has an adverse effect on the surface properties of the slab strand and further shortens the life of the mold.

In order to prevent the occurrence of abrasion on the long side wall of the mold in the continuous casting method with application of a static magnetic field, the present inventors pulled the long side walls of the mold in the direction away from each other during the width change, thereby shortening the length of the mold. A method of changing the mold width in which the clamping force of the mold long side wall sandwiching the side wall is reduced, and at least one of the mold short side walls is moved along the width direction of the mold long side wall while maintaining this state. (JP-A-4-327343).

Although the above technique was effective as a method for preventing the occurrence of scratches on the long side walls of the mold based on the mutual attraction of the long side walls of the mold due to the magnetic force, the inventors of the present invention have described the details of the scratches. After investigating the cause of the occurrence, even if the suction force between the long side walls was reduced by the above-mentioned technology, the scale was attracted to the long side walls by magnetic force, and this was still different because it was bitten into the gap between the long side and the short side. It was found that scratches occurred.

Therefore, the present inventors have studied a mold width changing method capable of effectively preventing the above two types of scratches.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and prevents the occurrence of abrasions on the walls of the long side walls of the mold, thereby changing the width of the mold during casting in continuous casting capable of extending the life of the mold. It is intended to provide a method (hereinafter also referred to as a width change).

[0007]

According to a first aspect of the present invention, in a continuous casting of steel for casting a slab while applying a static magnetic field across a long side of a mold, the casting width is changed in advance during casting. Reducing the speed to a speed at which no inclusion defects occur in the absence of a magnetic field application, then stopping the application of the magnetic field,
A method of changing the width of a mold in continuous casting, comprising changing the width of the mold, resuming the application of a magnetic field after the width change is completed, and then increasing the casting speed to the casting speed during application of a normal magnetic field.

In a second invention, in a continuous casting of steel in which a slab is cast while applying a static magnetic field across the long side of the mold, when changing the mold width during the casting, the casting speed is previously reduced before the casting speed is reduced. The casting speed is reduced to 9/10 or less of the casting speed, then the application of the magnetic field is stopped, the mold width is changed, and after the width change is completed, the application of the magnetic field is restarted. This is a method for changing the mold width in continuous casting, characterized by increasing the casting speed to the casting speed.

In the second aspect of the invention, when changing the mold width during casting, it is more preferable to reduce the casting speed in advance to 4/5 to 9/10 of the casting speed before the casting speed was reduced. If the casting speed is reduced to less than 4/5, productivity is undesirably reduced. On the other hand, if it exceeds 9/10, the inclusion flow causes inclusions to be entangled, which impairs the quality of the slab.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. In general, in the casting speed control of the continuous casting machine, when changing the width, control is performed such that the target speed is changed after the width change is completed. Also, when changing the width when applying a magnetic field in the mold, the casting speed is controlled by the above-described method while the magnetic field is applied.

FIG. 2 (a) is a plan view showing the configuration of a variable width continuous casting mold. Also, FIG.
A partial enlarged view of part A of FIG. FIG.
In FIGS. 1A and 1B, reference numerals 1a and 1b denote a pair of long-side walls made of copper and water-cooled mold fixedly held on a mold frame Mf so as to face each other (hereinafter also referred to as long-side walls), 2a and 2b. Is a pair of short side walls (hereinafter also referred to as "short side walls") of a pair of copper and water-cooled molds sandwiched between the long side walls 1a and 1b, and a continuous casting mold M is formed by a combination thereof.

Reference numerals 3a and 3b denote magnetic poles for applying a static magnetic field, which are arranged on the back of the long side walls 1a and 1b with the long side walls interposed therebetween and control the flow of molten steel in the mold M. Also, 4a, 4b are short side walls 2a,
In the driving device 2b, the short side walls 2a, 2b are moved along the width direction X of the long side walls 1a, 1b by the operation of the driving devices 4a, 4b to change the width W of the continuous casting mold M.

As a result of detailed investigation of the mechanism of occurrence of scratches on the mold long side walls 1a and 1b, the present inventors found that the short side copper plates of the mold short side walls 2a and 2b and the mold long side wall during the mold width change. 1a, 1b Scale etc. bites into gaps 7a, 7b, 8a, 8b with long side copper plate,
The gap was opened, and it was found that scales and the like further bite into the widened gap, causing scratches on the long side walls 1a and 1b of the mold and shortening the life of the mold.

[0014] It has also been clarified that the biting of the scale and the like is caused by the scale adhered to the long side walls 9a and 9b of the mold by the magnetostatic force. In addition, as a method of preventing biting of the scale or the like, before changing the width, in advance, the casting speed is reduced to a speed at which no inclusion defect occurs when no magnetic field is applied, and after reaching the casting speed, By stopping the application of the magnetic field and changing the width, the mold long side walls 1a, 1b
It was found that it was possible to prevent the occurrence of scratches on the slab and to prevent the occurrence of inclusion defects in the slab strand.

The width change in continuous casting which can prevent both the occurrence of scratches on the long side wall of the mold and the generation of inclusion defects in the strand of the slab, based on the results of elucidating the mechanism of occurrence of the scratches on the long side wall of the mold. The method is described. The present invention, based on the newly obtained knowledge described above, when changing the width during the casting of the continuous casting machine, do not apply a magnetic field during the width change, and further, the casting speed before the start of the width change After the speed is reduced and the width is changed, a magnetic field is applied to increase the casting speed.

FIG. 1 shows an example of a method for controlling the magnetic field strength (magnetic flux density) (a) and the casting speed (b) in the width changing method during casting in the continuous casting of the present invention. That is,
According to the present invention, as shown in FIG. 1, when performing the width change during casting, the speed is reduced to the target casting speed at the time of stopping the application of the magnetic field before the start of the width change, and then at or before the start of the width change. The application of the magnetic field was stopped, the mold width was changed, the application of the magnetic field was restarted at or after the end of the width change, and then the casting speed was increased to the target casting speed when the magnetic field was applied. The scale and the like attached to the mold no longer bite into the gaps 7a, 7b, 8a, 8b between the short side copper plate and the long side copper plate during the movement of the mold short side walls 2a, 2b, and the mold long side wall surfaces 9a, 9b Generation of abrasion can be prevented.

According to the present invention, the application of the magnetic field is stopped while the application of the magnetic field is stopped during the width change, and the casting speed is previously reduced to the target casting speed (maximum regulated speed) when the application of the magnetic field is stopped. It has become possible to prevent the occurrence of quality defects in the slab strand at the time of stoppage, and to minimize the reduction in productivity. The target casting speed (maximum regulated speed) when the application of the magnetic field is stopped is desirably a speed that does not cause inclusion defects when no magnetic field is applied. In the present invention, preferably, the casting speed before the casting speed is reduced is reduced. The casting speed is preferably 9/10 or less, and more preferably 4/5 to 9/10 of the casting speed before the casting speed was reduced.
More preferred.

[0018] This is because if it exceeds 9/10, inclusion defects will occur, and if it is less than 4/5, the productivity will decrease.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. (Example) Using the continuous casting mold shown in FIG. 1 described above, the magnetic poles 3a and 3b arranged on the back of the mold long side walls 1a and 1b were used.
Continuous casting of a slab strand having a thickness of 260 mm and a width of 1000 mm was performed at a casting speed of 2.0 m / min while applying a static magnetic field at a magnetic flux density of 0.3 T (tesla).

Next, after reducing the casting speed to 1.7 m / min, the application of the magnetic field was stopped, and the mold width was changed to 900 mm. After changing the mold width, the application of a magnetic field with a magnetic flux density of 0.3 T (tesla) was resumed, and then the casting speed was increased to 2.0 m / min.
Speed increased. In addition, the casting speed at the time of the above-mentioned deceleration, the required quality as a cold-rolled steel sheet obtained by hot rolling and cold rolling of the slab manufactured by the preliminary experiment and the occurrence of inclusion defects when no magnetic field is applied It is a casting speed based on a relational expression with no casting speed, in which no inclusion defect occurs when no magnetic field is applied.

As a result of repeating the above-mentioned operation experiments five times, in all the experiments, all the obtained slab strands did not show any deterioration of the surface properties due to scratches on the long side wall of the mold. Also, almost no inclusion defects were found in the cold-rolled steel sheet obtained by hot rolling and cold rolling from the slab. (Comparative example) Operated by applying and stopping the magnetic field, changing the mold width, and applying the magnetic field (restarting the application of the magnetic field) under the same conditions as in the above example, except that the casting speed was always constant at 2.0 m / min. An experiment was performed.

As a result, the entire slab strand obtained is
Deterioration of the surface properties due to abrasion of the long side wall of the mold was not observed at all, but inclusion defects such as burrs and blisters occurred in the cold-rolled steel sheet.

[0023]

According to the present invention, it is possible, for the first time, to extend the life of a mold and to always maintain good quality of a slab strand during continuous casting, and its industrial effect is great.

[Brief description of the drawings]

FIG. 1 shows the magnetic flux density in the mold width changing method of the present invention.
6 is a graph showing an example of a method for controlling the casting speed (a) and the casting speed (b).

FIG. 2 is a plan view showing the configuration of a variable width continuous casting mold.
(a) and the partial enlarged view of the A section (b).

[Explanation of symbols]

 1a, 1b Mold long side wall 2a, 2b Mold short side wall 3a, 3b Magnetic pole 4a, 4b Drive 5 Tie rod 6 Shaft 7a, 7b, 8a, 8b Clearance between short side copper plate and long side copper plate 9a, 9b Mold long side wall Wall f Frame M Continuous casting mold Mf Mold frame W Width of continuous casting mold

Claims (2)

[Claims] 1. In continuous casting of steel in which a slab is cast while applying a static magnetic field across the long side of a mold, when changing the width of the mold during casting, the casting speed must be set in advance when no magnetic field is applied. Decelerate to a speed that does not cause object defects, then stop applying the magnetic field, change the mold width, resume the application of the magnetic field after the width change is completed, and then reduce the casting speed during the normal magnetic field application A method for changing the mold width in continuous casting, characterized by increasing the speed up to 2. In continuous casting of steel in which a slab is cast while applying a static magnetic field across the long side of the mold, when changing the width of the mold during casting, the casting speed is previously set to the value of the casting speed before the casting speed is reduced. Decelerate to 9/10 or less, then stop applying the magnetic field, change the mold width, restart the application of the magnetic field after the width change, and then increase the casting speed to the casting speed during normal magnetic field application. A method for changing a mold width in continuous casting, characterized by speeding up.